petroleum refining is petroleum refining

Something that contains no petroleum is petroleum-free.

Petroleum is a liquid.

A. E. Dunstan has written:

'The science of petroleum' -- subject(s): Petroleum engineering, Petroleum industry and trade

'Chemistry and the petroleum industry' -- subject(s): Petroleum

Norman J. Hyne has written:

'Geology for petroleum exploration, drilling, and production' -- subject(s): Petroleum, Prospecting, Petroleum engineering, Geology

'Dictionary of petroleum exploration, drilling & production' -- subject(s): Dictionaries, Petroleum, Petroleum engineering

'Nontechnical guide to petroleum geology, exploration, drilling, and production' -- subject(s): Prospecting, Petroleum, Petroleum engineering, Geology